Process for low-phosphorus ferromanganese alloys



ited States atent Patented Mar. 6, 1962 1 2 3 024 105 -To render the alloy poorer in its phosphorus content, While maintaining the desired silicon content it is neces- PROCESS FOR LOW-PHOSPHORUS FE ROM N SE ALLOYS sary to control also the composition of the slag in such a August M. Kuhlrnan, Niagara Falls, N.Y., assignor to Union Carbide Corporation, a corporation of New York No Drawing. Filed Nov. 23, 1960, Ser. No. 71,170

1 Claim. (Cl. 75-1335) The present invention relates to an improved metallurgical process for the production of low-phosphorus ferromanganese alloys.

Ferromanganese alloys which are low in phosphorus are extremely well suited for manganese additions to molten steel baths because, besides producing steels which contain very small amounts of phosphorus, they allow the utilization of the silicon contained therein for the reduction of metal oxides and their transfer from the slag back into the metal bath, thus increasing considerably the recovery of the primary metals.

Deposits of manganese-bearing ores, which contain high percentages of phosphorus, often in amounts exceeding one percent, constitute a large portion of the available manganese. These deposits were, heretofore, of limited usefulness because of the diflicult and uneconomical techniques of removing the phosphorus therefrom. At present, it is general practice to select manganese ores which are satisfactorily low in phosphorus, the acceptable phosphorus level in most alloys being of the order of about 0.2 percent or less. There exists a need for a process to produce alloys with such acceptable phosphorus levels by economically utilizing the vast phosphorus-rich manganese deposits.

It is, accordingly, an object of the present invention to provide an improved process of producing low-phosphorus ferromanganese alloys from high-phosphorus manganese ores.

Other objects and advantages of the present invention will be apparent from the following description and appended claim.

Briefly stated, the process which satisfies the objects of the invention comprises smelting in a metallurgical furnace a mixture composed of a high-phosphorus manganese ore, sufiicient silica alumina, and calcium oxide and suflicient additional carbonaceous material to produce an alloy containing from about 35 to about 40 percent silicon, and a slag having a composition of from about 25 to about 60 percent alumina, from about 25 to about 40 percent calcium oxide, up to 20 percent by weight silica, and having a ratio of alumina to calcium oxide of at least 1.0; and tapping the molten mass at temperatures of from about 1640 C. to about 1720 C., whereby a ferromanganese alloy containing less than one percent of phosphorus is produced.

The process of the invention is essentially a one-stage process in which a manganese-ore containing high percentages of phosphorus is smelted in a metallurgical furnace, such as, for example, a covered electric furnace, under controlled conditions of slag composition and temperature of tapping.

It has been observed that the phosphorus content in the final ferromanganese alloy is controlled partly by the silicon content in the alloy and partly by the temperature of the melt which, in turn, is governed by the composition of the slag. Thus, for example, it has been found that alloys prepared by smelting a mixture containing silica in amounts sufiicient to introduce in the alloy the required quantity of silicon, but disregarding the critical requirements of the slag composition, possess quantities of phosphorus of the order of about five to eight-tenths of one percent by weight.

manner that tapping of the molten metal may be effected "at between about 1640 C. and about 1720 C. It has been found that a slag having a composition of from about 25 to about 60 percent by weight alumina, from about 25 to about 40 percent by weight calcium oxide, up to about 20 percent by Weight silica, and having a ratio of alumina to calcium oxide of at least 1.0 governs the tapping temperature in such a manner that a final alloy having from about 35 to about 40 percent by weight silicon and 0.2 percent or less by weight phosphorus may be obtained at tapping temperature of from about 1640 C. to about 1720 C., the correct temperature to be employed depending on the corresponding slag composition. Employment of tapping temperatures substantially outside the range set forth hereabove results in a final alloy which does not contain the required and specified silicon and/or phosphorus amounts.

Manganese ores of high phosphorus content vary considerably in their gangue constituents, so that, as mentioned above, additions of slag-forming materials have to be eifected in order to obtain, upon smelting, a slag composition within the range necessary to achieve a tapping temperature of from about 1640 C. to about 1720 C. which, in turn, results in a final ferromanganese alloy containing from about 35 to about 40 percent silicon and a fraction of one percent phosphorus.

To illustrate the process of the invention, a mixture was prepared comprising Parts by weight Belgian Congo manganese ore concentrate (Mn 50.4%, Fe 2.1%, SiO 4.4%, A1 0 5.2%, P

0.12%) 353.5 Brazilian hematite (Fe O 97.1%, Si0 1.0%, A1 0 1.6%, P 0.10%) 312.5 Quartz 181.2 Bauxite (15% moisture) 35.5 Phosphate rock (18.4% P) 50.4 Lime 9.0

This mixture was mixed with 508.8 additional parts by weight of quartzite and 525.0 parts by weight of carbonaceous matter (255 parts of Buckwheat coke and 270 parts of Pocahontas coal) and furnaced.

The smelting was carried out in a submerged arc furnace using a round 30-inch diameter shell lined with carbon paste and a single 12-inch graphite electrode. The metal and slag resulting from the smelting were tapped at 1645 C. into cone pots lined with a silica sand-clay slurry. The final alloy resulting from the process was found to consist of by weight:

Percent Silicon 35.2 Manganese 31.0 Phosphorus 0.085 Incidental impurities 1.0 Iron balance carbonaceous reducing agent to introduce from about 35 to 40 percent by weight of silicon into said ferromanganese alloy and up to 20 percent by weight silica, from about 25 to about 60 percent by weight alumina, and from about 25 to about 40 percent by weight calcium oxide into said slag, the weight ratio of alumina to calciumoiride in said slag being at least 1.0, and tapping the smelted mixtu're at altemperature in the range of about l64 O C. to about 1720 C. whereby a ferromanganese alloy containing less than one percent of phosphorus is produced.

No references cited. 

